The present invention relates to optical discs such as compact discs (xe2x80x9cCDsxe2x80x9d) and digital versatile discs (xe2x80x9cDVDsxe2x80x9d), which are used to store digital and digitized information such as computer software, video and sound recordings. More particularly, the present invention relates to an improved method and apparatus for manufacturing such discs.
DVDs and CDs are used as a storage media for digital and digitized information. Digital data is physically stored on these discs and more specifically on an information layer on such discs. The disc information layer contains digital data pits which are three-dimensional micron sized pits containing the digitized information. These discs store large amounts of information. In the case of DVDs, some formats may carry up to 28 gigabytes of video, music or software. Optical discs are typically read with CD players, DVD players, or ROM disc drives. A laser device in the disc players read the data via a laser beam. In this method, the laser sends out a light beam and a sensing device receives a reflected signal from the disc information layer.
Optical discs such as DVDs and CDs are typically made from one or more component discs of optical grade polycarbonate. In the process of manufacturing an optical disc, a nickel stamper (a metal matrix that contains digital data in the form of data pits and protrusions) is used to form an information carrying layer in the polycarbonate. Specifically, polycarbonate is injected into a mold holding a nickel stamper. A negative image of the pits is formed in the polycarbonate during the molding process. The molded image which consists of data pits is subsequently covered with a reflective coating. The reflective coating is sealed with a protective layer, such as a lacquer or the like.
A typical CD or DVD manufacturing process involves the steps of input data preparation, glass mastering, metalization and galvanics, and disc replication. The input data preparation process involves preparing digital tape or CD-R that contain digital data encoded according to a known error correction standard.
During the glass mastering process, the digital data is input into a computing device of a laser beam recorder. This involves a laser xe2x80x9cburningxe2x80x9d digital data pits in a uniform layer of photo-resist that covers the top surface of a glass master. Typically, glass masters are manufactured from highly polished, circular glass pieces (for example, 240 mm in diameter and 6 mm thick) covered with a layer of photo-resist material. The glass mastering process involves laser beam recording or conversion of digital data into geometrically shaped data pits. The data pits are formed in the photo-resist layer covering the glass master""s top surface. Subsequently, the photo-resist covered glass master surface is vacuum metalized (with silver, nickel, or other suitable materials) to make it electrically conductive. Once vacuum metalized, the glass master is ready for use in the electro-forming process of creating a nickel stamper.
The metalization and galvanics process of forming a nickel stamper involves glass master vacuum metalization (with a silver or nickel layer) and subsequent xe2x80x9ccopyingxe2x80x9d of the glass master via a galvonic or electro-forming process. The data pits in the glass master are precisely replicated in the electro-forming process as nickel ions are gradually dissolved in a nickel sulfate solution and deposited over the electrically conductive surface of the glass master. After the desired stamper thickness is achieved (determined by a current/time/deposition rate calculation according to Faraday""s law), the glass master and stamper are removed from the electro-forming galvanic cell. Subsequently, the nickel stamper is separated from the surface of the glass master. The nickel stamper, a negative copy of the glass master, contains the xe2x80x9creverse imagexe2x80x9d data pits of the glass master. The nickel stamper is circular, flat, electrolytic nickel substrate approximately 140 mm in diameter and 300 microns thick.
The disc replication process involves taking a previously prepared nickel stamper and inserting into a disc mold of an injection-molding machine. During the injection molding process, plastic discs are replicated. These plastic discs are typically made of polycarbonate or acrylic. The replicated discs represent xe2x80x9ca plastic copyxe2x80x9d of the nickel stamper which contains the digital data. The discs are then vacuum metalized with a thin layer of aluminum, silver, or gold. The metalized discs are protected with a coating of UV curable resin to prevent metal corrosion. In the case of DVDs, additional pressing is required in the form of disc bonding. The disc bonding process is required since the DVD discs are constructed from two halves, both of which may contain digital data information. The discs are then decorated, packaged and shipped to distributors, retailers or consumers.
The various molding machines capable of producing CDs and DVDs are generally very expensive and inefficient. The optical disc market expects to increase substantially mainly due to the proliferation of DVD video and CD/DVD-R applications.
The demands for faster, less expensive optical discs with increased data density necessitate the improved manufacturing of such discs. As described above, the disadvantages of a lengthy, labor intensive and complicated manufacturing process are unacceptable. Accordingly, there is a need for an improved method and apparatus for manufacturing optical discs.
The present invention provides an improved method and apparatus for manufacturing optical discs by applying at least one data containing information layer on at least one side of a support substrate. The present invention provides applying at least one data containing information layer on at least one side of a support substrate. The apparatus and method of the present invention separates the typical optical disc manufacturing process into two steps by applying an information layer to a previously manufactured support substrate, instead of molding a support substrate and information layer together in one step.
The apparatus for applying at least one data information layer on at least one side of a support substrate to produce an optical disc may be called a xe2x80x9cSpin-On Information Layerxe2x80x9d (xe2x80x9cSPOILxe2x80x9d) station. A SPOIL station includes a support plate attached to a rotatable shaft that may be connected to an electric motor or other device for rotating the apparatus about a vertical axis. The support plate has a top surface for supporting a stamper, ultraviolet (xe2x80x9cUVxe2x80x9d) curable resin, and a support substrate. The UV curable resin forms the information layer on the support substrate of the optical disc. The stamper has a first side and a second side opposite the first side. The second side has digital information in the form of data pits. In use, the stamper is placed onthe top surface of the support plate, with the first side of the stamper placed against the top surface of the support plate. UV curable resin is applied to the second side of the stamper. The support substrate is placed on the second side of the stamper with the UV curable resin sandwiched in-between. The stamper is preferably held on the support plate by vacuum or magnetic force during rotation of the apparatus to uniformly spread the UV curable resin between the stamper and support substrate.
A method of manufacturing optical discs using the above-described apparatus comprises the following steps: placing a stamper on a support plate of the apparatus; depositing an UV curable resin on the top surface of the stamper; placing a support substrate on top of the stamper with the UV curable resin sandwiched in-between; rotating a rotatable shaft of the apparatus about a vertical axis to spread the resin onto both surfaces of the support substrate and stamper; exposing the joined surfaces of the support substrate and stamper to UV radiation; removing the newly formed optical disc comprising the support substrate and the UV cured resin information layer from the surface of the stamper; vacuum metalizing the optical disc, especially the information layer with a reflective coating; and, sealing the metalized disc with a protective coating. The newly formed optical disc comprises a support substrate and an information layer, with the information layer containing data pits precisely replicated from the data pits of the stamper.
A second embodiment of the apparatus of the present invention consists of a multi-position spin station for manufacturing more than one optical disc at a time. The apparatus includes at least one stamper spin station, at least one stamper changing device, and at least one UV curing station. The multi-position manufacturing apparatus significantly increases optical disc manufacturing throughput, and allows for an uninterrupted disc manufacturing process.
The dimensional precision of data pits replicated with the SPOIL process is generally equal to or better than data pits formed by a standard injection molding process. Furthermore, vacuum metalized optical discs made from the SPOIL process exhibit better than average optoelectric characteristics.
Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof.